Wireless communications systems, such as two-way radio systems, have to accommodate widely varying demands. One source of variation is the widely varying number of mobile communication devices that may wish to receive service from one access point, such as a base station, at different times. Another source of variation is the widely varying asymmetry between the amount of data that any particular user may download from an access point, and the amount of data that the same user may need to upload to the access point.
Some wireless communication systems such as LTE and 802.11 are able to provide high download speeds to multiple mobile communication devices, using over-the-air multicast/broadcast service. A typical application is the streaming of video. However, although multicast has been a part of the 802.11 standard since its inception, it is not widely deployed. Notably, it is useful only when a large audience is anticipated to view the same content at approximately the same time.
802.11 multicast includes no provisions for retransmission of lost packets. As a consequence, in a situation in which there is a random dispersion of mobile devices around an access point, a modulation of suitably low complexity must be selected, in order to ensure a relatively low packet error rate. For example, BPSK or QPSK modulation may be selected BPSK or QPSK modulation will, reliably, achieve a packet error rate of 10−3 or better. However, the use of a low complexity modulation, when applied to high data rate streams such as video, can result in very high channel utilization.
In some 802.11 systems, there may be multiple non-overlapping channels available in both the 2.4 and 5 GHz bands. Additionally, some known single access points may be able to provide service across multiple channels simultaneously, for example in one channel in the 2.4 GHz band and another channel in the 5 GHz band.
A mobile communication device can typically only maintain an association with a single access point and a single channel at a time. However, situations arise where there are a multitude of high data rate streams available to mobile communication devices. Since a network designer doesn't know which mobile stations are attached to which access points, and which high data rate streams they may want to consume, all such streams must presently be made available from all access points. Multiplexing and transmitting two or more high data rate streams on the same 802.11 channel using multicast with low complexity modulation, however, will require an appreciable reduction of quality of each stream. If the high data rate streams are video, then their quality may be reduced to standard definition resolution, when two or more are multicast on one 802.11 channel. In addition, multicasting the two or more video streams on one 802.11 channel will limit or entirely negate use of the channel for other data access.
Modern 802.11 networks may be implemented in areas where many users and their mobile communication devices are located in a relatively small area. These networks may be arranged with geographically overlapping coverage of different access points on differing channels. So, at most times, one mobile communication device will be within range of two or more access points. The differing channels here might, for example, be the 2.4 GHz Channels 1, 6, and 11. Such a network provides more throughput per unit area, assuming that there is client load balancing across channels. In this arrangement, any given mobile communication device can normally rely on access to two or more 802.11 channels at any given location within the network.
FIG. 1 illustrates coverage in a known wireless communication system 100. The wireless communications system 100 may, for example, be an LTE or 802.11 network. There is overlapping coverage within wireless communications system 100. The three channels STA1, STA2, or STA3 are repeated access the network. However, in the illustrated example, no two neighbouring access points transmit the same channel.
Each dashed circle 110, 120 in FIG. 1 illustrates the coverage area of a particular access point. The channel provided within each dashed circle 110, 120 is indicated by the lettering STA1, STA2, or STA3 within the hexagon located at the centre of the circle. Dashed circle 110 is the extent of coverage of a channel STA1 from one access point. Dashed circle 120 is the extent of coverage of a channel STA2 from another access point.
A mobile communication device located within wireless communications system 100 can typically receive two or more of channels STA1, STA2, or STA3 at any one time. Wireless communications system 100 may typically assign a mobile communication device to receive the channel from the access point that provides the strongest signal to the mobile communication device, subject to suitable load sharing between the various access points.
The operator of a network such as that in FIG. 1 may provide users with access to two or more data streams. One or more of the data streams may, for example, be video streams. This situation should be a perfect use case for 802.11 multicast, such that multiple users can watch the same video stream at roughly the same time, without additional bandwidth cost. However, the video content is sourced from an application server in the communications network, and application servers have no knowledge of 802.11 channels. In reality, therefore, the 802.11 channels can become quickly overloaded in such systems, as multiple video streams are requested by mobile communications devices operating on the same 802.11 channel. Once again, the result is that each mobile communication device receives lower quality video stream, and channel capacity for other data access by other users is lowered.
Accordingly, there is a need for an improved multicast wireless communication system.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.